Molecular analysis of population genetic variability and insecticide resistance of the yellow fever mosquito in Trinidad and Tobago - abstract

Spatial patterns of genetic variants in natural populations are the combined effects of various evolutionary forces and demographic structure. Population life history and mating structure have genome-wide effect, but selection, affects only the target loci or closely-linked loci. This study examines the spatial patterns of 4 natural Aedes aegypti populations of Trinidad and Tobago, through registration fragment length polymorphism (RFLP) analysis of 16 genetic loci representative of mosquito genome on 870 individuals. These populations have been subjected to numerous organophosphate (OP) insecticides for more than 2 decades, but have not been subjected to DDT over this period. We predicted that genes closely-linked to the OP target loci would be strongly affected in gene polymorphism, and probably be the most differentiated loci in the genome, but gene flow has homogenized frequencies for the gene conferring resistance to DDT. As predicted, low DNA polymorphisms and gene deletions were found for loci in the general chromosomal region of the OP target site, and these exhibited large scale FST value. The gene conferring resistance to DDT shows similar polymorphisms and genetic differentiation to other loci in the genome. We concluded that gene flow was not sufficiently frequent to prevent genetic differentiation due to genetic drift or selection, but could be a powerful force for the spread of insectide resistance genes. (AU)

Seasonal abundance, biting cycle and parity of the mosquito Haemagogus leucocelaenus in Trinidad, West Indies

Adult female populations of Haemagogus leucocelaenus (Dyar and Shannon), the sylvan vector of yellow fever, were monitored weekly during 1981-82 by human collectors on the ground at Point Gourde in Chaguaramas Forest, 16 km west of Port-of-Spain, Trinidad. Hg.leucocelaenus showed only diurnal landing activity, from 06.00 to 18.00 hours (sunrise to sunset, universal time), with a single peak of activity between 10.00 and 14.00 hours. Densities of Hg.leucocelaenus during the wet season (May-November) were about double the level recorded during the dry season (December-April). Monthly parous rates averaged 53.9 percent (range 25-90 percent) and some females were up to five pars. Retained eggs (range 2-6, mean 4/female) were found in the ovaries of 0.34 percent of landing females, all of which had stage 1 ovarian follicles for the next gonotrophic cycle. Therefore blood-feeding is not inhibited by egg retention. Hg.leucocelaenus vector potential is reappraised in the light of these findings (AU)

Congenital yellow fever virus infection after immunization in pregnancy

To determine whether yellow fever (YF) vaccine administered in pregnancy causes fetal infection, women who were vaccinated during unrecognized pregnancy in a mass campaign in Trinidad were studied retrospectively. Maternal and cord or infant blood were tested for IgM and neutralizing antibodies to YF virus, indicating congenital infection. The infant, the first repotred case of YF virus infection after immunization in prgnancy, was delivered after an uncomplicated full-term pregnancy and appeared normal. Congenital dengue 1 infection may have occurred in another case. The frequency of fetal infection and adverse events after such exposure could not be estimated; however, the neurotropism of YF virus for the developing nervous system and the now documented possibility of trans-placental infection underscores the admonition that YF vaccination in pregnancy should be avoided (AU)

Studies on the natural history of yellow fever in Trinidad

This small monograph is more than simply a collection of papers about yellow fever, it is also an expression of the origins of the Caribbean Epidemiology Centre (CAREC). Although many early accounts recorded in these pages cannot be scientifically authenticated, research this century suggests a cyclic pattern of epizootics with occasional outbreaks of human disease. The natural cycle of the disease involves monkeys and mosquitoes but mysteries remain to be elucidated, such as where does the virus go between epizootics. Transovarial transmission among mosquitoes may be important, while other mammalian and insect species might also be involved. Such questions are raised in these pages

Emergency vector control of urban vectors during an epizootic of yellow fever in Trinidad: 1988-1989

Sylvatic yellow fever outbreaks in Trinidad have been known to occur since the 17th century. During 1988-89 an outbreak of yellow fever occurred with the virus being isolated from monkeys and mosquitoes. This article summarizes the vector control operations adopted to prevent urban transmission of the yellow fever virus by Aedes aegypti Linn. No human cases of yellow fever were detected either in the rural or urban areas (AU)

Yellow fever studies in Trinidad, 1988-1989: attempts to demonstrate Transovarial Transmission of yellow fever virus in Haemagogus mosquitoes collected in nature

Subsequent to an epizootic of yellow fever (YF) in monkeys and the isolation of yellow fever (YF) virus from sylvatic mosquitoes in December, 1988 and January, 1989 in south-east Trinidad, ovitrapping for mosquito eggs was started in January, 1989, in an attempt to demonstrate transovarial transmission of the virus. Multi-paddle ovitraps were used. From a total of 52,632 eggs collected in various parts of the country, the following species of mosquitoes were reared: Haemagogus janthinomys (54 percent), Hg. leucocelaenus (32 percent), Aedes insolitus (12 percent), Hg. equinus (1 percent). When mosquito eggs were removed from the hard board paddles then vacuum-treated for hatching, the process proved very economical in storage space. Most eggs were obtained at the start of the wet season, four to five months after the isolation yellow fever virus from wild caught adult mosquitoes and monkey carcasses. When adult mosquitoes reared from eggs were processed for yellow fever virus, no virus was detected from any of the mosquito pools to indicate that transovarial transmission had occurred (AU)

Sylvatic yellow fever activity in Trinidad 1988-1989

Of a total of 18,068 mosquitoes (361 pools) collected in south-eastern Trinidad forests from December, 1988 to May, 1989, 47 species belonging to 14 genera were identified. Five yellow fever virus isolates were made from Haemagogus janthinomys and one from Sabethes chloropterus. All the other pools of mosquitoes examined were negative for the virus. The mosquito isolates were made in December and January. In addition, in late February and early March, two infected howler monkeys (Alouatta sp.) were detected. Since March, despite continued surveillance, no yellow fever virus has been detected in mosquitoes or monkeys. There has been no reported human infection (AU)

The 1988-1990 epizootic of yellow fever in Trinidad: virological aspects

Sylvatic yellow fever virus activity occurred in Trinidad between December, 1988 and January, 1990. It was first detected in the Trinity Hills area of Guayaguayare in the south eastern forest of the island and subsequently spread west to Moruga and north to Fishing Pond. Surveillance activities in these areas resulted in the collection of over 18,000 mosquitoes and seven monkeys which were referred to the CAREC laboratories for viral investigation. Six pools of mosquitoes yielded yellow fever virus in December, 1988 and January, 1989. Isolations were made from Haemagogus janthinomys (five pools) and Sabethes chloropterus (one pool). Extensive collections in other areas failed to yield virus. Three Alouatta monkeys proved to be infected with yellow fever. These were all Alouatta sp. and were submitted to the laboratory in February and March of 1989 and January of 1990. Thorough virological investigation of febrile persons, with and without liver involvement, showed no evidence to spread to the human population either before or during the epizootic. This was attributed to the high level of immunization achieved in the population following the yellow fever outbreak of 1978-1980 (AU)

Surveillance for Alouatta monkeys in the forests of Trinidad, 1988-1989

A continuous surveillance programme for the presence of the red howler monkeys (Alouatta sp.) in the forests of Trinidad was initiated following an epizootic of yellow fever in these monkeys in 1978. This paper gives the result of the programme from 1986 to 1989 (AU)

Aedes aegypti surveillance at the airports in Trinidad and Tobago: an eight year study

A Programme of surveillance for Aedes aegypti mosquitoes was instituted at the airports of Trinidad and Tobago following an epidemic of yellow fever in 1978. The Surveillance system consisted of the use of ovitraps to collect Ae. aegypti eggs. After a period of eight years and the examination of 54,136 ovitrap paddles, 53 paddles were found positive. Only one of the positives came from Tobago. In Trinidad, ovitraps set in the car park and areas easily accessible to the general public were the ones most frequently found positive for Ae. aegypti eggs. The quick detection of positive paddles and close liaison with the Ministry of Health allowed prompt treatment of the affected areas, reducing the risks of possible transport of these mosquitoes by aircraft to other countries (AU)

Studies on yellow fever in inter-epizootic period in Trinidad

Following an outbreak of yellow fever in Trinidad in 1978-1979, a study was undertaken to investigate the jungle reservoirs and vectors of yellow fever virus in the inter-epizootic period, to seek evidence of natural transovarial transmission of yellow fever virus in Haemagogus collected. These were made four months after the last detection of virus in that area of the island and could not positively be attributed to transovarial transmission. None of the 42,815 progeny of wild mosquitoes yielded virus. No yellow fever virus was isolated from 34,300 mosquitoes other than Haemagogus nor from 15 vertebrates collected in areas of former virus activity. Good progress was made in optimizing the use of the AP-61 cell line resulting in rapid isolation and identification of dengue and yellow fever viruses from Caribbean countries (AU)

An assessment of the yellow fever vaccination campaign in Trinidad, West Indies

A study was undertaken to assess the effectiveness of a yellow fever vaccination campaign, which had been conducted in Trinidad, West Indies from November, 1978 through 1979. Evaluative tools consisted of: (i) an interview survey in a randomly selected sample of two hundred households, to determine immunization coverage and (ii) a serological study of 232 vaccines to ascertain protection conferred through use of 17D yellow fever vaccination. Results of the household survey indicate that approximately 12.53 percent of the 1149 persons interviewed had not been vaccinated against yellow fever. In most instances, no substantial reasons could be advanced by respondents for non-immunization. Based on the performance of 13 plaque reduction neutralization tests, all but one of the 232 sera examined from people with a history of immunization posessess adequate humoral immunity to yellow fever. This study has, therefore, shown that the vaccination campaign, under review, was successful in achieving satisfactory protection of immunized persons, and in drastically reducing the number of susceptibles within the population (AU)

Yellow fever immunization activities, 1979

Short account of immunization activities and campaign during the yellow fever outbreak in Trinidad 1979

Vector control operations during a sylvatic yellow fever outbreak in Trinidad,1978-1980

An outline is given of the vector control measures adopted during the 1978-1980 yellow fever epidemic in Trinidad and the efficacy of the yellow fever plan of action is discussed (AU)

Yellow fever: evolution of ideas concerned with demonstrating the natural occurrence of transovarial transmission of virus in mosquitoes

In November 1978, an outbreak of disease among wild simians of south Trinidad alerted officials to the presence of jungle yellow fever (YF). Learning of the epizootic and having recently been involved in studies establishing transovarial transmission (TOT) of YF virus, this laboratory urged Trinidad workers to undertake demonstration of the natural occurence of TOT in the forest environment. The idea as well as a suggested procedural protocol involving vector mosquitoes (Haemagogus spp.) was accepted and acted upon. Initial procedures called for undertaking studies in areas where sick or dead monkeys were observed, collecting larvae as well as adult female Haemagogus from which eggs were to be obtained, hatched, and the ensuing larvae reared to adults and tested for virus. As time passed, various problems were encountered necessitating changes in field procedures. The most important was the substitution of ovitraps for adult female collections as a source of eggs. By 1980, the epizootic/epidemic was waning. Funding for additional studies became available from Canadian sources and the author was invited to be a consultant. Field and laboratory procedures were again modified and streamlined. Described are: (1) choice of field sites, (2) choice of ovitraps, (3) siting of ovitraps, (4) frequency of collections, (5) laboratory procedures, (6) search for male Haemagogus and female ovipositing activity, and (7) duration of a TOT study and conclusions (AU)

An innovative approach to non-human primate census

A low altitude aerial transect censusing of howler monkeys was conducted on the Chaguaramas Peninsula. This method of censusing has proven to be more advantageous than the more frequently used ground transect census. During a three hour period, 138 monkeys were counted in a 972 hectare area (AU)

Monitoring of Alouatta monkeys as an early warning system in yellow fever surveillance

An epizootic of yellow fever occurred in Alouatta monkeys in November 1978. An intensive surveillance programme was initiated to locate sick and dying monkeys in the forests of Trinidad. Thirty Alouatta (red howler)monkeys were collected and examined for yellow fever virus. Sixteen of the monkeys were positive for the virus and these came from south-east, east, and north-west Trinidad (AU)

A clinico-pathological study of yellow fever with demonstration of the virus in the human liver

The clinical histopathological and serological findings in three patients who developed yellow fever after entering the Guayaguayare forest in south-east Trinidad in January and February 1979 are described in this report. The patients were all previously healthy young males and the clinical features of the disease varied from fulminant viral hepatitis with hepato-renal failure to a self-limiting anicteric viral illness. The first patient died, and histopathological examination of the liver was done post-mortem. Needle biopsy of the liver was done on case 2 which presented with the clinical picture of infective hepatitis, and on case 3 with the features of an anicteric viral illness. The histopathological hallmarks of midzonal necrosis, granular eosinophilic degeneration (Councilman bodies) and fatty change in the parenchymal cells of the liver were seen in three cases. The electron microscopic study demonstrated the presence of the yellow fever virus in the liver of the patient who died (AU)

Laboratory diagnosis of yellow fever infections in humans, alouatta monkeys and haemagogus mosquitoes in Trinidad, 1978-1980

The yellow fever epidemic in Trinidad began with an epizootic in alouatta monkeys in November, 1978. Activity was detected by virus isolation from Alouatta monkeys and from Haemagogus mosquitoes between this date and July 1980. First reports of monkey deaths centered around the Guayaguayare forests of South Trinidad, following which the epizootic spread west to the Moruga area, and north through the Biche Forest reserve, eventually reaching the north-west Chaguaramas peninsula. Surveillance of febrile persons attending clinics and hospitals was intensified and 18 confirmed cases were identified, from 14 of whom yellow fever virus was isolated. In four cases, diagnoses were made on the basis of liver pathology only. Paired sera were obtained from 10 of 11 persons who survived, and in each case serological conversions were obtained by haemagglutination inhibition and mouse neutralization tests. Yellow Fever virus was isolated from 16 of 32 Alouatta monkeys and from 19 of 174 pools of Haemagogus mosquitoes. Two systems were used for virus isolation: the Aedes cell line AP-61 and suckling mice. The former proved to be more sensitive, detecting virus in 11.7 percent of 725 specimens inoculated whereas suckling mice detected virus in 7.9 percent of 724 specimens. In 11 instances virus was detected in an animal or mosquito pool by AP-61 but not initially by mouse inoculation whereas the converse was true in only one case (AU)

Yellow fever in Trinidad and Tobago 1978-1980: epidemiological aspects

Between 1978-1979 an epidemic of yellow fever occurred in Trinidad in two phases. Eight cases occurred in December 1978-March 1979 and 10 cases occured in August-September 1979. Seven died, giving a case fatality rate of 39 percent. All cases were male aged 16-58 years (median 22.5). Seventeen had been exposed in forests where the virus was active and none had records of being vaccinated. The high level of clinical and virological surveillance that existed made it likely that all or nearly all the cases were ascertained. Intense immunization, health education and vector control efforts also mitigated against a larger epidemic (AU)